Measurements of the Carrier Dynamics and Terahertz Response of Oriented Germanium Nanowires using Optical-Pump Terahertz-Probe Spectroscopy

摘要

We have measured the terahertz response of oriented germanium nanowires usingultrafast optical-pump terahertz-probe spectroscopy. We present results on thetime, frequency, and polarization dependence of the terahertz response. Ourresults indicate intraband energy relaxation times of photoexcited carriers inthe 1.5-2.0 ps range, carrier density dependent interband electron-holerecombination times in the 75-125 ps range, and carrier momentum scatteringrates in the 60-90 fs range. Additionally, the terahertz response of thenanowires is strongly polarization dependent despite the subwavelengthdimensions of the nanowires. The differential terahertz transmission is foundto be large when the field is polarized parallel to the nanowires and verysmall when the field is polarized perpendicular to the nanowires. Thispolarization dependence of the terahertz response can be explained in terms ofthe induced depolarization fields and the resulting magnitudes of the surfaceplasmon frequencies.